This invention relates generally to a method and apparatus for separating material from a fluid, and more particularly relates to an apparatus for recovering precious metals such as gold, silver, platinum or other dense solids from placer deposits in a liquid passing through a conduit.
Historically, devices such as a sluice have been used to recover placer gold from streams of water. Rainwater runoff and gravitational attraction move placer material downhill to a stream in valleys below. Logs or other barriers generate riffles in the stream. A screen is anchored below these riffles to retain the gold. In the gold recovery art, free gold accelerates downhill at a greater rate than aggregates, and a turbulence is needed to temporarily separate the gold from the fast moving stream. In this process the gold is trapped immediately to prevent the journey of the gold downstream and away.
Modern sluices use the basic concept and method of an open trough that is oriented downhill. A turbulent generating device, such as riffles, is provided over a retainer material which is anchored below.
Conventional sluice boxes, rockers and dry washers are used today to separate material while the solids travel down an incline plane through an open channel sluice. These modern devices take advantage of high vertical acceleration rate of dense particles through the fluid. However, when down slope paths are employed, dense solids also accelerate linearally at a higher rate than less dense solids. Due to the force of gravity, carrier fluid and solid materials' linear velocity increases throughout the flow path. Riffles placed in the path of the sluices create turbulence which generates a local low velocity and low pressure downstream to slow the dense solids. Immediate entrapment of the dense solids is critical to capturing these solids. The small dense particles remain suspended in the turbulent fluid and are lost.
A drawback to modern material removers is that linear acceleration of water also accelerates the dense solid material along the flow path and hinders the separation process. To perform proper separation, it is necessary to decelerate the velocity of gold while at the same accelerating unwanted solids.